Hello
>Can someone live with 1100 b.p. in Gibraltar? Pay one's rent, bills and going out?
Yes. If you are single, don't have a car and expensive habits, plus you don't mind living 20 minutes walk from Gibraltar across the border in Spain, you would be absolutely fine.
> How many salaries do you have (12, 13 or 14?)
12, one every month, or 52, one every week (depending on your employer). Some companies offer annual bonus, but this can vary from 100 pounds to many thousands, it's entirely up to the employer and your performance at work and there is no "standard" 13th salary once a year.
>Is there any website where I can calculate how much clean salary will I have in the end of each month, after tax is deducted?
Here is a good calculator:
gibraltarinsurance.gi/calculators-inctax.asp
>Is there any airline which flights directly from Athens, Greece?
No.